I'm amazed you actually have access to someone who works on poultry! But maybe waiting to see the vet until the choking stops isn't the best strategy if you are able to get him help now. Sounds like the poor guy is suffering badly.
Hoping for the best.
If the extra tissue in your duck's throat is inflamed and exacerbating the coughing/choking episodes, maybe you should try the anti-inflammatory you mentioned being able to get and see if that helps.
Good to know! I searched a bit more and found the reference I quoted above if anyone wants specifics (I think I actually got this link through another thread in this forum). https://shagbarkbantams.com/the-many-uses-of-oxine-ah-animal-health/
I can't find the info with recommendation I quoted, and what I find now indicates the activator is required, so I'm retracting this statement to be on the safe side.
Did you get your Oxine AH online? I'm looking for a reliable source. Would like to try it in my livestock water tanks to keep scum and algae growth down. Asked my vet but she has never heard of it.